Re: [PATCH v2 1/3] jump_label: Add static_key_fast_inc()

On 11/3/22 21:41, Peter Zijlstra wrote:

On Thu, Nov 03, 2022 at 09:25:22PM +0000, Dmitry Safonov wrote:

quoted

A helper to add another user for an existing enabled static key.

Utter lack of clue what for.

quoted

+/***
+ * static_key_fast_inc - adds a user for a static key
+ * @key: static key that must be already enabled
+ *
+ * The caller must make sure that the static key can't get disabled while
+ * in this function. It doesn't patch jump labels, only adds a user to
+ * an already enabled static key.
+ */
+static inline void static_key_fast_inc(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE(key);
+	WARN_ON_ONCE(atomic_read(&key->enabled) < 1);
+	atomic_inc(&key->enabled);
+}

And no, that's racy as heck. We have things like atomic_inc_not_zero(),
I suggest looking into it.

Thanks for the review, I'll look into that for v3.

Thanks,
          Dmitry